The present invention relates to a magnetic field-enhanced plasma etch reactor and to associated processes for etching substrate materials.
Magnetic field-enhanced etch reactors for plasma etching of a substrate are well known. In such reactors, a magnetic field perpendicular to an electric field in a cathode plasma sheath can enhance plasma density. In this regard, the dense plasma is usually located at an east side of the magnetic field lines due to what is commonly referred to as the ExB drift providing a higher etch rate in that area. In an attempt to produce uniform etching, such reactors commonly employ a rotating magnetic field to average out plasma density differences. Such a rotating magnetic field is generated using two pairs of electromagnets on opposite sides of the reactor chamber containing the substrate to be etched. The magnetic field produced by current flowing in one pair of coils is perpendicular to the other. When the pairs of coils are driven by sinusoidal currents which are 90 degrees out of phase, a rotating magnetic field is created parallel to the upper surface of the substrate in the reactor chamber.
Even with plasma reactors employing such a rotating magnetic field, nonuniform plasma densities and etch rates persist and substrates processed in such reactors still exhibit undesirable non-uniform etch patterns. In particular, on the substrates processed by such magnetic field-enhanced plasma reactors, such non-uniformities and differences commonly occur in particular regions such as the four corner regions of the upper surface of the substrate between adjacent electromagnets. In addition, electrical components on such substrates are subject to charge up damage due to non-uniform plasma density. Further, such nonuniform plasma densities often result in (i) differences in "selectivity" of etch rate on the substrates, (ii) differences in residue deposit distribution on the substrate and (iii) differences in corrosion or erosion on the substrate. Such non-uniformities and differences also may be found on the surfaces of the hardware comprising such reactors including the reactor chamber surfaces, gas distribution plate, cathode pedestal components and so on.
A unique reactor system having the capability of instantaneously and selectively altering the magnetic field strength and direction is described in commonly assigned U. S. Pat. No. 4,842,683 issued Jun. 27, 1989 and entitled "Magnetic Field-Enhanced Plasma Etch Reactor". The patent is incorporated herein by this reference both for completeness of the description of the background of this invention and also for completeness of the detailed description hereinafter set forth. The unique magnetic field-enhanced reactor described in the patent improves the uniformity of the resulting etch patterns on substrates processed by the reactor.
Despite the improvements represented by the above-referenced patent, non-uniform plasma density and etch rates persist and the resulting etch patterns still regularly exhibit non-uniformities of about 6% or more where non-uniformity is defined as the maximum etch rate minus the minimum etch rate divided by twice the mean etch rate over the entire area of the etched surface of the substrate. Therefore, there is continuing need to provide a magnetic field enhanced plasma etch reactor and associated processes which will regularly produce more uniform plasma densities and etch rates and etch patterns with non-uniformities of less than 6%. The present invention satisfies such requirements.